Jackson’s move, announced Wednesday, is being welcomed by the environmental community and children’s health advocates. Perchlorate, a major component of rocket and missile propellants and many explosives, is a potent thyroid toxin known to disrupt brain and neurological development. For that reason, scientists and medical experts strongly urge that fetal and neonatal exposures to the chemical be prevented.

Defense and aerospace contractors are certain to fight any federal effort to order up perchlorate clean-ups, whose costs could run into the tens or hundreds of millions of dollars. During the Cold War, tons of improperly stored rocket fuel seeped into ground waters around rocket and missile test sites and chemical manufacturing and storage facilities.

As David Corn, Washington bureau chief of Mother Jones reported last February, companies that make or use perchlorates have hired a “bevy of lobbyists,” among them Democrats such as former Nevada senator Richard Bryan, once a leading advocate for safe drinking water, to fend off stringent EPA measures.

MoJo updates its coverage this week by reporting that “lobbyists for perchlorate firms are well-funded and skilful—and those with Democratic ties, like Bryan, will arguably wield more influence in Obama’s Washington than they did during the era of Republican dominance. They’ll doubtless be working hard behind the scenes to head off the EPA’s new regulatory enthusiasm.”

During the Bush administration, EWG and other environmental health advocates, including the agency’s own Children’s Health Protection Advisory Committee, mounted futile efforts to persuade EPA leaders to crack down on perchlorate pollution.

Marty and her fellow panel members protested the agency’s assumption that perchlorate contamination of up to 15 micrograms per liter of water posed no threat to adults or even children. The agency’s failure to take into account differences between adult and children, she wrote, “does not recognize the science which supports the exquisite sensitivity of the developing brain to even small drops in thyroid hormone levels and the fact that neonates have much diminished stores of thyroid hormone relative to adults.” Without legal strictures and a much lower permissible perchlorate limit, she wrote, thousands of infants could be at risk for “life-long consequences of impaired brain development.”

Jackson’s announcement called for public comments over the next 30 days. She did not prejudge the outcome. But her carefully-worded statement sent a strong signal. It made clear that she and her aides had studied the Marty panel’s arguments closely and recognized their validity.

“It is critically important to protect sensitive populations, particularly infants and young children, from perchlorate in drinking water,” Jackson said.

She said she had ordered EPA staffers to place “special emphasis on evaluating the impact of perchlorate on infants and young children.” Moreover, she said, EPA calculations will “take…into account the fact that infants and children consume more water per body weight than do adults” and to consider “a broader range of alternatives for interpreting the available data on the level of health concern, the frequency of occurrence of perchlorate in drinking water, and the opportunity for health risk reduction through a national primary drinking water standard.”

If, as Jackson seems to be semaphoring, EPA is heading toward regulating perchlorate pollution, and presumably clean-up efforts, the effort will amount to a direct challenge to defense and aerospace contractors — who can be expected to make the EPA struggle for every inch of turf.

How fiercely and skillfully Jackson, and ultimately the Obama administration, counter the industries’ formidable legal and lobbying defenses will tell us a lot about the Obama presidency. The stakes are enormous. Is the administration willing to spend some of its political capital on this issue? Will it even have enough political capital left after the bruising health care and climate bill battles? There’s no way to answer these questions today. But very possibly, soon.